1. General Transcription Factors (GTFs):
* TFIID: Binds to the TATA box (a DNA sequence) within the promoter region of a gene. This is essential for positioning RNA polymerase correctly.
* TFIIA and TFIIB: Help stabilize TFIID binding and recruit RNA polymerase II to the promoter.
* TFIIH: Has multiple functions, including unwinding the DNA double helix to allow access for RNA polymerase, and phosphorylating the tail of RNA polymerase II to initiate transcription.
* TFIIE and TFIIF: Assist in recruiting and stabilizing RNA polymerase II, and play a role in initiation and elongation.
2. Enhancers and Transcriptional Activators:
* Enhancers: DNA sequences that can be located far from the gene they regulate. They bind to transcriptional activators (proteins) which can interact with the GTFs and RNA polymerase II to further enhance transcription.
* Transcriptional Activators: These proteins often bind to specific DNA sequences, leading to conformational changes in chromatin structure and facilitating the recruitment of the GTFs and RNA polymerase II.
3. Chromatin Remodeling Complexes:
* Chromatin: Eukaryotic DNA is wrapped around histone proteins, forming a compact structure called chromatin. This structure can inhibit access to DNA for transcription.
* Chromatin Remodeling Complexes: These protein complexes modify the structure of chromatin by altering histone modifications or moving nucleosomes, making the DNA more accessible for transcription.
4. RNA Processing Factors:
* Capping Enzymes: Add a 5' cap to the mRNA molecule, which is essential for stability, translation, and nuclear export.
* Splicing Factors: Carry out splicing, removing introns (non-coding regions) from the pre-mRNA and joining exons (coding regions) to create a mature mRNA molecule.
* Polyadenylation Factors: Add a poly-A tail to the 3' end of the mRNA, providing stability and regulating translation.
In summary, transcription in eukaryotes requires a sophisticated system of protein factors that work together to initiate, regulate, and process gene expression. These factors bind to DNA, interact with each other, and modify chromatin structure, ensuring the accurate and efficient transcription of genes.
